In contemporary communication systems, radio frequency receivers or transmitters receive or transmit an RF (radio frequency) signal using an antenna that is directly coupled via discrete components (usually a RF matching network) to the input or output of an amplifier of a receiver or transmitter, respectively.
Presently, there are two configurations for antennae on RF transceivers: internal and external. Internal antennae are typically much less efficient at transferring power to or from the transceiver because of their physical size (they must fit inside the housing) and the effective radio frequency loading presented to the antenna by the housing and nearby electronic components. Conversely, external antennae do not exhibit as much degradation in efficiency and maintain their directivity (pattern and gain) better than an internal antenna since they are located primarily in free space. That is, they are not surrounded by a housing. By locating the antenna in free space, the effects of loading caused by the radio's housing and components are minimized.
When designing a radio device, if the required system power gain dictates that a more efficient antenna is required, the designer is forced to trade off an increase in the overall physical dimensions of the device in order to use a high gain, high efficiency antenna system. However, previous attempts to improve receiver sensitivity or a transmitter's ERP (effective radiated power) in a portable RF transmitter or receiver with an internal antenna have centered around the physical and electrical attachment of another independent antenna structure to a port coupled to the unit's existing antenna system or amplifier connection port. Although some of these attempts have been operationally successful to some degree, problems associated with imperfect, complicated, and expensive physical contacting schemes remain. These problems include (but are not limited to) the loss of an effective RF electrical contact at the antenna interface resulting from vibration, corrosion, or improper assembly. Other problems that arise when coupling directly to an existing antenna system are de-tuning and skewing the frequency response of the existing antenna as well as altering the impedance, thus degrading the overall performance of the overall antenna system even though an external antenna has been added to the system.